The present invention relates to an optical apparatus having a contrast improvement function and to a contrast improvement method, and more particularly relates to contrast improvement of an image in optical equipment such as microscopes, cameras and the like.
It is known in the art of optics that the contrast in the images formed by optical apparatus can be improved by inserting a filter having a particular transmittance distribution in the pupil (i.e., Fourier) plane of the apparatus. Such a technique is discussed, for example, in the book Theory of Fourier Imaging, by Teruji Ose, published by Kyoritsu Shuppan, 1979, on pages 98-107. This contrast improvement method works by tailoring the optical transfer function (OTF) of the optical system to be applicable to the spatial frequency of interest.
A problem with this technique, however, is that certain objects (e.g., specimens in a microscope) have features with many different spatial frequencies. Thus, while contrast is improved at certain spatial frequencies, the contrast at other spatial frequencies is degraded.
The present invention relates to an optical apparatus having a contrast improvement function and to a contrast improvement method, and more particularly relates to contrast improvement of an image in optical equipment such as microscopes, cameras and the like.
The present invention takes into consideration the aforementioned problem, and has the objective to provide an optical apparatus having a contrast improvement function, and a contrast improvement method that can improve the contrast for specific frequency characteristics as well as overall image characteristics.
Accordingly, a first aspect of the invention is an optical apparatus capable of providing a contrast-improved image of an object. The apparatus comprises an illumination optical system including a light source that condenses light from the light source to illuminate the object. Adjacent the illumination system is an objective optical system having a transform plane and an image plane. A pupil modulating filter is arranged at the transform plane and has a transmittance distribution capable of being varied from a first transmittance distribution to a second transmittance distribution so as to respectively form first and second images at the image plane. A detector is located at the image plane to detect the first and second images. Electrically connected to the detector is an image synthesizer for synthesizing the first and second images to form the contrast-improved image.
A second aspect of the invention is the optical system as described above, wherein the pupil modulation filter comprises a first filter having the first transmittance distribution and a second filter having the second transmittance distribution. The pupil modulation filter is designed such that the first and second filters may be selectively arranged in the transform plane.
A third aspect of the invention is a method of improving the contrast of an image of an object in an image-forming optical apparatus having a transform plane and an image plane. The method comprises the steps of first illuminating the object and forming a first image of the object at the image plane. This is achieved by passing light from the object through the optical apparatus and through a first transmittance distribution created at the transform plane. The next step is detecting and storing the first image. The next step is forming a second image of the object at the image plane by passing light from the object through the optical apparatus and through a second transmittance distribution created at the transform plane. The next step is detecting and storing the second image. Then, the final step is synthesizing the first and second images to form the contrast-improved image.